1. Field of the Invention
The present invention relates to a fuel pump control apparatus of an engine, and more particularly, to a fuel pump control apparatus of an engine for small outboard motor unfurnished with a battery and getting the engine started by manually rotating a crank shaft.
2. Background Art
For an outboard motor for small boat having a relatively small displacement, a carburetor system is the mainstream of a fuel supply. An outboard motor adopts a device configuration furnished with neither a battery nor a starter and thereby getting the engine started by a manual operation of a ship operator using a recoil starting device, that is, a typical outboard motor is relatively lightweight and gets the engine started at a low cost. However, with the aim of enhancing ease of operation and maintenance, emission control, and output performance, shifting from the carburetor system to an FI (Fuel Injection) system is taking place for a fuel supply in an outboard motor for small boat having a small displacement.
Even in such a case, an outboard motor is often furnished with neither a starting device, such as a starter, nor a battery to form a compact and light engine at a low cost. The outboard motor uses injectors that supply the engine with a fuel, a fuel pump, a fuel pressure regulator that maintains a fuel pressure at a certain pressure, a sensor that detects an operation condition of the engine, and an ECU (Electronic Control Unit) as a controller that carries out fuel control. Also, the outboard motor is furnished with a power generator that supplies these components with power and thereby supplies the engine with a fuel by activating the ECU and the injectors on the power from the power generator while the engine is driven.
Meanwhile, there is a strong demand for power saving arising from environmental issues, such as global warming, and it becomes necessary to drive a fuel pump in an efficient manner such that suppresses an energy loss (current consumption and fuel heat generation). To this end, there is proposed a fuel supply apparatus (see Patent Document 1) configured to control a fuel pressure supplied to the injectors to be maintained at a required target value by carrying out feedback (F/B) control on a driving current of a fuel pump from the viewpoint of efficiently supplying the engine with a minimum amount of fuel close to an amount of fuel the engine requires by enhancing fuel supply accuracy of the fuel pump.
According to the method proposed in Patent Document 1, in order to enhance a response in transition when the target value of the fuel pressure is changed, an amount of fuel to be supplied to the engine is calculated on the basis of a rotation speed and a load condition of the engine and a driving current is controlled to temporarily exceed the changed target current value in the changed direction. Accordingly, because a larger driving amount has to be provided to the fuel pump, a wasteful loss occurs in current consumption and a self-generated voltage is consumed considerably. The proposed method therefore has a problem that it does not match up with the demand of power saving.
In addition, because an amount of fuel to be supplied to the engine by the fuel pump is determined according to data pre-set in the ECU, it is difficult to adjust an amount of fuel by quickly responding to irregularities among parts involved with an actuator and a change of the engine condition. Hence, accuracy above a certain degree cannot be achieved with a unique map value. Further, because a current obtained by power generation is consumed by a load on the fuel pump when a larger driving amount than is essentially necessary is set in driving duty data, the power generator attached to the fuel supply apparatus has to have a large generation capacity.
Moreover, a temperature of the motor itself rises due to current consumption by the fuel pump and the parts undergo a temperature-induced drift. This results in a problem that even when the fuel pump is driven by the same driving amount, because motor rotations differ from pump characteristics of the driving duty, the same result cannot be obtained.
In a case where the fuel pump apparatus is used for another engine having a different displacement, data on the fuel pump driving duty is set on the basis of an amount of fuel the engine requires together with the driving characteristics of the fuel pump. In this case, it is necessary to set the data system by system and there arises a problem that man-hours are increased to make fuel pump apparatus available for another engine.
Patent Document 1: JP-A-11-247695